Known devices of this kind, such as disclosed in DE-PS No. 29 19 209, have proven useful in particular because a single power drive suffices for the respective functions of raising and transporting, selectively, a print or a correction ribbon. In U.S. Pat. No. 4,407,594 also showing a device of this kind, a magnet to switch from the one to the other operating mode is required in addition to a motor. However, in both of these known devices the print ribbon returns to its basic position after each reproduction of a character. This means a slower typing speed, which has a negative effect especially when the machine is used as printer in data processing or the like. Moreover, in a device according to the noted DE-PS No. 29 19 209, a relatively strong motor must be used because the type-wheel with its drive must also be raised together with the print and correction ribbons. This, too, influences the typing speed negatively.
Also in co-pending application of Manfred Hubner et al, Ser. No. 667,577, filed Nov. 2, 1984, titled Print and Correction Ribbon Drive System, mechanisms of the above kind are also disclosed wherein the various functions for both the print and correction ribbon are driven by a single motor. There, provision is made to maintain the ribbon at the typed line level when the machine is operated at high rates of printing, e.g., printer applications, while the transport steps are being carried out. However, in this mechanism, a special clutch and a precisely working change gear mechanism is required. In addition, quite a number of components are necessary which must be produced and assembled. Therefore, from the aspect of design, this mechanism is less suited for small typewriters intended for use in printer applications.
An object of the invention is in the provision of improved mechanism for raising and transporting print and correction ribbons requiring a relatively weak motor and which can be accomodated on the carriage of a type carrier.
Another object of the invention is in the provision of mechanism wherein the functions of raising and transporting the print ribbons are performed sequentially and wherein provision is made to maintain the print ribbon in raised position so that the motor need only drive the print ribbon transport during rapid printing.
Another object of the invention is in the provision of mechanism to raise and transport a print or a correction ribbon selectively by means of cams and cam followers according to the direction of rotation of a motor and in the provision for locking the print ribbon in raised position by means of the cam drive.
A still further object of the invention is in the provision of mechanism for raising and transporting print and correction ribbons by means of a motor driven cam and cam followers wherein the length of the transport steps is adjustable according to the angle through which the cam is driven .